1. Field of the Invention
The present invention relates to a manufacturing device and manufacturing method for a liquid crystal display panel and a liquid crystal display panel and more particularly to a spacer spraying system to spray spacers on a substrate of a liquid crystal display panel and a method for spraying the spacers on the liquid crystal display panel substrate and to a liquid crystal display panel having the liquid crystal display panel substrate manufactured by using the above spacer spraying system and the above method.
The present application claims priority of Japanese Patent Application No. 2004-221637 filed on Jul. 29, 2004, which is hereby incorporated by reference.
2. Description of First Related Art
A liquid crystal display panel is widely used as a display device for an AV (Audio-Visual) apparatus, an OA (Office Automation) apparatus, and a like due to its advantages of being thin, light weight, low in power consumption, and a like. The liquid crystal display panel of this type is made up of a TFT (Thin Film Transistor) substrate in which switching elements such as TFTs or a like are formed in a matrix form and a facing substrate in which a color filter, black matrix, or a like are formed. Insulating spacers made of polymer beads, silica beads, or a like, each having a specified size are arranged between both the substrates to form a gap having a specified size which is filled with a liquid crystal sealed hermitically therein. The liquid crystal display panel is so configured that an image is displayed by applying a voltage to an electrode formed on a pair of substrates facing each other or on one of the substrates to generate an electric field and by controlling an orientational direction of the liquid crystal according to the electric field to change transmitivity of light. In the liquid crystal display panel having such configurations as above, it is important that, in order to improve displaying quality, the gap between substrates facing each other is formed uniformly and, therefore, the spacers used to form the gap are sprayed uniformly on the substrates.
There are two methods of spraying the spacers on the substrates; one is a wet spraying method in which a spacer-containing solvent obtained by dispersing the spacers in the solvent for example flon (fluoro carbon), alcohol, or a like is jetted from a nozzle and the other is a dry spraying method in which the spacers are charged by an electrostatic charge process using an electrostatic gun or contact friction and the charged spacers are jetted from the nozzle. In the case of the wet spraying method, collection of flon, alcohol, or a like is required and the spacers are easily condensed in the solvent and, therefore, it is difficult to spray the spacers uniformly on the substrate and, as a result, the dry spraying method is widely used.
In the case of the dry spraying method, in ordinary cases, the spacers are positively charged and a repulsive force is exerted among the spacers and, therefore, partial condensation of the spacers does not occur, however, since a central portion of a stage is located immediately below the nozzle, an amount of the sprayed spacers tends to increase. On the other hand, since a distance between a peripheral edge portion of the stage and the nozzle increases at the central portion of a stage, the amount of the sprayed spacers tends to decrease at the peripheral edge portion of the stage, thus causing the sprayed spacers to be not uniform in a density distribution on an entire of the stage depending on a positional relation between the nozzle and the stage.
In order to improve such uniformity of a spacer spray density distribution caused by the positional relation between the nozzle and the stage, a method is disclosed in which a chamber of a spacer spraying system is charged so as to have a potential with the same polarity (positive polarity in ordinary cases) as that of the charged spacers, and the charged spacers being released in a direction of a charged wall of the chamber with the same polarity as the charged spacers are repelled from the charged wall of the chamber to a direction of the stage, thus enabling the spray density of the spacers to be distributed uniformly. For example, in Japanese Patent Application Laid-open No. 2002-148635, a spacer spraying system is disclosed in which a spraying chamber housing a substrate has a layer-stacked structure in which each layer is electrically insulated and a voltage having a potential with the same polarity as that of the spacers is applied from an outside to the most inner layer surface of the chamber to make the spacers travelling on surfaces of the chamber be repelled by the electrostatic force, thus enabling a amount of the sprayed spacers in a peripheral edge portion of the substrate to be reduced.
Though non-uniformity in a density distribution of the sprayed spacers caused by the positional relation between the above nozzle and the stage can be improved by using the spacer spraying system disclosed in the Japanese Patent Application Laid-open No. 2002-148635, the amount of the spacers that gather around the peripheral edge portion of the stage by electrostatic repulsion from the chamber wall increase. To solve this problem, by adjusting a level of a voltage to be applied to a wall surface of the chamber and/or by improving a shape of a nozzle used to spray the spacers or a spray pattern of spacers or a like, amounts of the sprayed spacers in the peripheral edge portion of the stage placed near the chamber wall are calibrated, however, even if such adjustments are made, it is impossible to uniformly control the density distribution of the sprayed spacers on the substrate.
The reason for the above is that the density distribution of the sprayed spacers is varied not only by a positional relation between the nozzle and the stage and/or the positional relation between the chamber wall and the stage but also by the positional relation between the stage and the substrate placed on the stage. More particularly, though an electric field is approximately constant in a central portion of the stage, the electric field is concentrated in an edge portion of the stage due to an edge effect, which causes the amount of the sprayed spacers to increase in the peripheral edge portion of the substrate located near the edge portion of the stage.
In the case where the liquid crystal display panel is small in size or there is a sufficient space in a position where the substrate is cut (that is, in the case where an interval between the liquid crystal display panels is large when a plurality of the liquid crystal display panels is produced by one piece of the substrate), since a distance between the edge portion of the substrate and the region where the liquid crystal display panel is formed can be made large, even if the spraying amounts of the spacers increase due to the edge effect, the influence caused by the increased amounts of the spacers can be made small in the region where the liquid crystal display device is formed. However, when the liquid crystal display panel is large in size and when many liquid crystal display panels are densely arranged on the substrate to achieve reduction in costs, inevitably, no sufficient space exists in the position where the substrate is cut and, as a result, the influence caused by the edge effect occurs even in the liquid crystal display panel forming region being located in the vicinity of the stage end.
In order to reduce the influence caused by the edge effect, a method is available in which the substrate is located far from the stage end by making the chamber or the stage larger in size. However, if the chamber is larger in size, the amount of the spacers that can be used during a one-time spacer spraying process increases, causing unnecessary consumption of high-priced spacers and an increase in costs in the manufacturing of the liquid crystal display panel. Moreover, a size of the liquid crystal display panel varies depending on each of products required by users and, if a distance between the stage end and the liquid crystal display panel forming region being located in the vicinity of the stage end also varies depending on each of the products, the spacer spraying density changes in every product and, as a result, variations in performance of the product occur.
3. Description of Second Related Art
As explained in the first related art, when a liquid crystal display panel is manufactured, it is of importance that a gap between a pair of substrates facing each other is uniform and, to achieve this, uniform spraying of spacers on surfaces of the substrates is required. Therefore, in the spacer spraying system of a type that applies a voltage to a chamber, by adjusting a level of a voltage to be applied to an inner wall of the chamber and by improving a shape of a nozzle to jet spacers or a pattern of spraying spacers, uniformity of sprayed spacers in a density distribution is improved.
For example, in a conventional spacer spraying system having dimensions as shown in FIG. 13A, when a voltage to be applied to an inner wall of the chamber is set at 4.0 kV, 7.0 kV, and 10 kV and a spraying mode for each of the voltages is set at a mode 2 and mode 3 as shown in FIG. 13B, respectively, spraying density of spacers corresponding to each distance from a substrate end is as shown in FIG. 14. Though the spacer spray density distribution can be changed by varying the applying voltage or the spraying mode, if the voltage on a wall surface of the chamber is made large (see, for example, “X” mark or “*” mark in FIG. 14), spraying density at the substrate end becomes larger. If the voltage on the wall of the chamber is made smaller (see triangular marks in black), though spraying density at the substrate end can be made somewhat smaller, spraying density in a position on an inner side of the substrate end (for example, 200 mm to 300 mm from the substrate end) becomes very small and, as a result, uniform distribution of the sprayed spacers cannot be obtained at any voltage and the tendency cannot be changed by a change in the spraying mode. The reason for that is that, in the method in which a voltage to be applied to the chamber inner wall is adjusted and/or a shape of the nozzle or a pattern of spraying spacers is improved, variations in spraying density caused by a positional relation between the nozzle and stage or between the chamber wall surface and the stage are merely reduced, and it is impossible to reduce variations caused by a positional relation between the stage and substrate formed on the stage, that is, variations in the spacer spraying density caused by concentration of an electric field at the stage end cannot be reduced.
Moreover, a method is proposed in which, by changing a voltage to be applied to a stage on which a substrate is formed, variations in spraying density of spacers are reduced. For example, a method is disclosed in Japanese Patent Application Laid-open No. 2000-275652 in which the stage is divided into a plurality of portions of the stage and each of the divided stages or each of some divided groups of the stages is set at a different potential. However, the purpose of the method disclosed in the above Patent Application is to improve distribution of spacers sprayed within an inner surface of the entire stage and, therefore, it is impossible to reduce variations in spacer spraying density caused by a positional relation between the stage and substrate formed on the stage, that is, variations in spacer spraying density caused by concentration of an electric field at an edge portion of the stage cannot be suppressed.